Localised face processing by the human prefrontal cortex: stimulation-evoked hallucinations of faces

Intracranial neural representation of phenomenal and access consciousness in the human brain

After more than 30 years of extensive investigation, impressive progress has been made in identifying the neural correlates of consciousness (NCC). However, the functional role of spatiotemporally distinct consciousness-related neural activity in conscious perception is debated. An influential framework proposed that consciousness-related neural activities could be dissociated into two distinct processes: phenomenal and access consciousness. However, though hotly debated, its authenticity has not been examined in a single paradigm with more informative intracranial recordings. In the present study, we employed a visual awareness task and recorded the local field potential (LFP) of patients with electrodes implanted in cortical and subcortical regions. Overall, we found that the latency of visual awareness-related activity exhibited a bimodal distribution, and the recording sites with short and long latencies were largely separated in location, except in the lateral prefrontal cortex (lPFC). The mixture of short and long latencies in the lPFC indicates that it plays a critical role in linking phenomenal and access consciousness. However, the division between the two is not as simple as the central sulcus, as proposed previously. Moreover, in 4 patients with electrodes implanted in the bilateral prefrontal cortex, early awareness-related activity was confined to the contralateral side, while late awareness-related activity appeared on both sides. Finally, Granger causality analysis showed that awareness-related information flowed from the early sites to the late sites. These results provide the first LFP evidence of neural correlates of phenomenal and access consciousness, which sheds light on the spatiotemporal dynamics of NCC in the human brain.

An integrative view of the role of prefrontal cortex in consciousness

The involvement of the prefrontal cortex (PFC) in consciousness is an ongoing focus of intense investigation. An important question is whether representations of conscious contents and experiences in the PFC are confounded by post-perceptual processes related to cognitive functions. Here, I review recent findings suggesting that neuronal representations of consciously perceived contents-in the absence of post-perceptual processes-can indeed be observed in the PFC. Slower ongoing fluctuations in the electrophysiological state of the PFC seem to control the stability and updates of these prefrontal representations of conscious awareness. In addition to conscious perception, the PFC has been shown to play a critical role in controlling the levels of consciousness as observed during anesthesia, while prefrontal lesions can result in severe loss of perceptual awareness. Together, the convergence of these processes in the PFC suggests its integrative role in consciousness and highlights the complex nature of consciousness itself.

Towards a pluralistic neurobiological understanding of consciousness

Theories of consciousness are often based on the assumption that a single, unified neurobiological account will explain different types of conscious awareness. However, recent findings show that, even within a single modality such as conscious visual perception, the anatomical location, timing, and information flow of neural activity related to conscious awareness vary depending on both external and internal factors. This suggests that the search for generic neural correlates of consciousness may not be fruitful. I argue that consciousness science requires a more pluralistic approach and propose a new framework: joint determinant theory (JDT). This theory may be capable of accommodating different brain circuit mechanisms for conscious contents as varied as percepts, wills, memories, emotions, and thoughts, as well as their integrated experience.

Twenty years of investigation with the case of prosopagnosia PS to understand human face identity recognition. Part II: Neural basis

Patient PS sustained her dramatic brain injury in 1992, the same year as the first report of a neuroimaging study of human face recognition. The present paper complements the review on the functional nature of PS's prosopagnosia (part I), illustrating how her case study directly, i.e., through neuroimaging investigations of her brain structure and activity, but also indirectly, through neural studies performed on other clinical cases and neurotypical individuals, inspired and constrained neural models of human face recognition. In the dominant right hemisphere for face recognition in humans, PS's main lesion concerns (inputs to) the inferior occipital gyrus (IOG), in a region where face-selective activity is typically found in normal individuals ('Occipital Face Area', OFA). Her case study initially supported the criticality of this region for face identity recognition (FIR) and provided the impetus for transcranial magnetic stimulation (TMS), intracerebral electrical stimulation, and cortical surgery studies that have generally supported this view. Despite PS's right IOG lesion, typical face-selectivity is found anteriorly in the middle portion of the fusiform gyrus, a hominoid structure (termed the right 'Fusiform Face Area', FFA) that is widely considered to be the most important region for human face recognition. This finding led to the original proposal of direct anatomico-functional connections from early visual cortices to the FFA, bypassing the IOG/OFA (lulu), a hypothesis supported by further neuroimaging studies of PS, other neurological cases and neuro-typical individuals with original visual stimulation paradigms, data recordings and analyses. The proposal of a lack of sensitivity to face identity in PS's right FFA due to defective reentrant inputs from the IOG/FFA has also been supported by other cases, functional connectivity and cortical surgery studies. Overall, neural studies of, and based on, the case of prosopagnosia PS strongly question the hierarchical organization of the human neural face recognition system, supporting a more flexible and dynamic view of this key social brain function.

Decoding internally generated transitions of conscious contents in the prefrontal cortex without subjective reports

A major debate about the neural correlates of conscious perception concerns its cortical organization, namely, whether it includes the prefrontal cortex (PFC), which mediates executive functions, or it is constrained within posterior cortices. It has been suggested that PFC activity during paradigms investigating conscious perception is conflated with post-perceptual processes associated with reporting the contents of consciousness or feedforward signals originating from exogenous stimulus manipulations and relayed via posterior cortical areas. We addressed this debate by simultaneously probing neuronal populations in the rhesus macaque (Macaca mulatta) PFC during a no-report paradigm, capable of instigating internally generated transitions in conscious perception, without changes in visual stimulation. We find that feature-selective prefrontal neurons are modulated concomitantly with subjective perception and perceptual suppression of their preferred stimulus during both externally induced and internally generated changes in conscious perception. Importantly, this enables reliable single-trial, population decoding of conscious contents. Control experiments confirm significant decoding of stimulus contents, even when oculomotor responses, used for inferring perception, are suppressed. These findings suggest that internally generated changes in the contents of conscious visual perception are reliably reflected within the activity of prefrontal populations in the absence of volitional reports or changes in sensory input.

The role of the prefrontal cortex in conscious perception is debated because of its involvement in task relevant behaviour, such as subjective perceptual reports. Here, the authors show that prefrontal activity in rhesus macaques correlates with subjective perception and the contents of consciousness can be decoded from prefrontal population activity even without reports.

Decoding rapidly presented visual stimuli from prefrontal ensembles without report nor post-perceptual processing

The role of the primate prefrontal cortex (PFC) in conscious perception is debated. The global neuronal workspace theory of consciousness predicts that PFC neurons should contain a detailed code of the current conscious contents. Previous research showed that PFC is indeed activated in paradigms of conscious visual perception, including no-report paradigms where no voluntary behavioral report of the percept is given, thus avoiding a conflation of signals related to visual consciousness with signals related to the report. Still, it has been argued that prefrontal modulation could reflect post-perceptual processes that may be present even in the absence of report, such as thinking about the perceived stimulus, therefore reflecting a consequence rather than a direct correlate of conscious experience. Here, we investigate these issues by recording neuronal ensemble activity from the macaque ventrolateral PFC during briefly presented visual stimuli, either in isolated trials in which stimuli were clearly perceived or in sequences of rapid serial visual presentation (RSVP) in which perception and post-perceptual processing were challenged. We report that the identity of each stimulus could be decoded from PFC population activity even in the RSVP condition. The first visual signals could be detected at 60 ms after stimulus onset and information was maximal at 150 ms. However, in the RSVP condition, 200 ms after the onset of a stimulus, the decoding accuracy quickly dropped to chance level and the next stimulus started to be decodable. Interestingly, decoding in the ventrolateral PFC was stronger compared to posterior parietal cortex for both isolated and RSVP stimuli. These results indicate that neuronal populations in the macaque PFC reliably encode visual stimuli even under conditions that have been shown to challenge conscious perception and/or substantially reduce the probability of post-perceptual processing in humans. We discuss whether the observed activation reflects conscious access, phenomenal consciousness, or merely a preconscious bottom-up wave.

Visual mental imagery: Inside the mind's eyes

What are mental images needed for? A variety of everyday situations calls for us to plan ahead; one of the clever ways our mind prepares and strategizes our next move is through mental simulation. A powerful tool in running these simulations is visual mental imagery, which can be conceived as a way to activate and maintain an internal representation of the to-be-imagined object, giving rise to predictions. Therefore, under normal conditions imagination is primarily an endogenous process, and only more rarely can mental images be activated exogenously, for example, by means of intracerebral stimulation. A large debate is still ongoing regarding the neural substrates supporting mental imagery, with the neuropsychological and neuroimaging literature agreeing in some cases, but not others. This chapter reviews the neuroscientific literature on mental imagery, and attempts to reappraise the neuropsychological and neuroimaging evidence by drawing a model of mental imagery informed by both structural and functional brain data. Overall, the role of regions in the ventral temporal cortex, especially of the left hemisphere, stands out unequivocally as a key substrate in mental imagery.

The Quest for Hemispheric Asymmetries Supporting and Predicting Executive Functioning

This narrative review addresses the neural bases of two executive functions: criterion setting, that is, the capacity to flexibly set up and select task rules and associations between stimuli, responses, and nonresponses, and monitoring, that is, the process of continuously evaluating whether task rules are being applied optimally. There is a documented tendency for criterion setting and monitoring to differentially recruit left and right lateral prefrontal regions and connected networks, respectively, above and beyond the specific task context. This model, known as the ROtman-Baycrest Battery to Investigate Attention (ROBBIA) model, initially sprung from extensive neuropsychological work led by Don Stuss. In subsequent years, multimodal lines of empirical investigation on both healthy individuals and patients with brain damage, coming from functional neuroimaging, EEG, neurostimulation, individual difference approaches, and, again, neuropsychology, so to "complete the circle," corroborated the functional mapping across the two hemispheres as predicted by the model. More recent electrophysiological evidence has further shown that hemispheric differences in intrinsic prefrontal dynamics are able to predict cognitive performance in tasks tapping these domain-general functions. These empirical contributions will be presented together with contrasting evidence, limits, and possible future directions to better fine-tune this model and extend its scope to new fields.

Does the Prefrontal Cortex Play an Essential Role in Consciousness? Insights from Intracranial Electrical Stimulation of the Human Brain

A central debate in philosophy and neuroscience pertains to whether PFC activity plays an essential role in the neural basis of consciousness. Neuroimaging and electrophysiology studies have revealed that the contents of conscious perceptual experience can be successfully decoded from PFC activity, but these findings might be confounded by postperceptual cognitive processes, such as thinking, reasoning, and decision-making, that are not necessary for consciousness. To clarify the involvement of the PFC in consciousness, we present a synthesis of research that has used intracranial electrical stimulation (iES) for the causal modulation of neural activity in the human PFC. This research provides compelling evidence that iES of only certain prefrontal regions (i.e., orbitofrontal cortex and anterior cingulate cortex) reliably perturbs conscious experience. Conversely, stimulation of anterolateral prefrontal sites, often considered crucial in higher-order and global workspace theories of consciousness, seldom elicits any reportable alterations in consciousness. Furthermore, the wide variety of iES-elicited effects in the PFC (e.g., emotions, thoughts, and olfactory and visual hallucinations) exhibits no clear relation to the immediate environment. Therefore, there is no evidence for the kinds of alterations in ongoing perceptual experience that would be predicted by higher-order or global workspace theories. Nevertheless, effects in the orbitofrontal and anterior cingulate cortices suggest a specific role for these PFC subregions in supporting emotional aspects of conscious experience. Overall, this evidence presents a challenge for higher-order and global workspace theories, which commonly point to the PFC as the basis for conscious perception based on correlative and possibly confounded information.

Hemispheric asymmetries in visual mental imagery

Visual mental imagery is the faculty whereby we can "visualize" objects that are not in our line of sight. Longstanding evidence dating back over thirty years has shown that unilateral brain lesions, especially in the left temporal lobe, can impair aspects of this ability. Yet, there is currently no attempt to identify analogies between these neuropsychological findings of hemispheric asymmetry and those from other neuroscientific approaches. Here, we present a critical review of the available literature on the hemispheric laterality of visual mental imagery, by looking at cross-method patterns of evidence in the domains of lesion neuropsychology, neuroimaging, and direct cortical stimulation. Results can be summarized under three main axes. First, frontoparietal networks in both hemispheres appear to be associated with visual mental imagery. Second, lateralization patterns emerge in the temporal lobes, with the left inferior temporal lobe being the most common finding in the literature for endogenously generated images, especially, but not exclusively, when orthographic material is used to ignite imagery. Third, an opposite pattern of hemispheric laterality emerges when visual mental images are induced by exogenous stimulation; direct cortical electrical stimulation tends to produce visual imagery experiences predominantly when applied to the right temporal lobe. These patterns of hemispheric asymmetry are difficult to reconcile with the dominant model of visual mental imagery, which emphasizes the implication of early sensory cortices. They suggest instead that visual mental imagery relies on large-scale brain networks, with a crucial participation of high-level visual regions in the temporal lobes.

Intracerebral electrical stimulation to understand the neural basis of human face identity recognition

Recognizing people's identity by their faces is a key function in the human species, supported by regions of the ventral occipito-temporal cortex (VOTC). In the last decade, there have been several reports of perceptual face distortion during direct electrical stimulation (DES) with subdural electrodes positioned over a well-known face-selective VOTC region of the right lateral middle fusiform gyrus (LatMidFG; i.e., the "Fusiform Face Area", FFA). However, transient impairments of face identity recognition (FIR) have been extremely rare and only behaviorally quantified during DES with intracerebral (i.e., depth) electrodes in stereo-electroencephalography (SEEG). The three detailed cases reported so far, summarized here, were specifically impaired at FIR during DES inside different anatomical VOTC regions of the right hemisphere: the inferior occipital gyrus (IOG) and the LatMidFG, as well as a region that lies at the heart of a large magnetic susceptibility artifact in functional magnetic resonance imaging (fMRI): the anterior fusiform gyrus (AntFG). In the first two regions, the eloquent electrode contacts were systematically associated with the highest face-selective and (unfamiliar) face individuation responses as measured with intracerebral electrophysiology. Stimulation in the right AntFG did not lead to perceptual changes but also caused an inability to remember having been presented face pictures, as if the episode was never recorded in memory. These observations support the view of an extensive network of face-selective VOTC regions subtending human FIR, with at least three critical nodes in the right hemisphere associated with differential intrinsic and extrinsic patterns of reentrant connectivity.

Cognitive and Emotional Mapping With SEEG

Mapping of cortical functions is critical for the best clinical care of patients undergoing epilepsy and tumor surgery, but also to better understand human brain function and connectivity. The purpose of this review is to explore existing and potential means of mapping higher cortical functions, including stimulation mapping, passive mapping, and connectivity analyses. We examine the history of mapping, differences between subdural and stereoelectroencephalographic approaches, and some risks and safety aspects, before examining different types of functional mapping. Much of this review explores the prospects for new mapping approaches to better understand other components of language, memory, spatial skills, executive, and socio-emotional functions. We also touch on brain-machine interfaces, philosophical aspects of aligning tasks to brain circuits, and the study of consciousness. We end by discussing multi-modal testing and virtual reality approaches to mapping higher cortical functions.

How is electrical stimulation of the brain experienced, and how can we tell? Selected considerations on sensorimotor function and speech

Electrical stimulation of the nervous system is a powerful tool for localizing and examining the function of numerous brain regions. Delivered to certain regions of the cerebral cortex, electrical stimulation can evoke a variety of first-order effects, including observable movements or an urge to move, or somatosensory, visual, or auditory percepts. In still other regions the subject may be oblivious to the stimulation. Often overlooked, however, is whether the subject is aware of the stimulation, and if so, how the stimulation is experienced by the subject. In this review of how electrical stimulation has been used to study selected aspects of sensorimotor and language function, we raise questions that future studies might address concerning the subjects' second-order experiences of intention and agency regarding evoked movements, of the naturalness of evoked sensory percepts, and of other qualia that might be evoked in the absence of an overt first-order experience.

Parallel and functionally segregated processing of task phase and conscious content in the prefrontal cortex

The role of lateral prefrontal cortex (LPFC) in mediating conscious perception has been recently questioned due to potential confounds resulting from the parallel operation of task related processes. We have previously demonstrated encoding of contents of visual consciousness in LPFC neurons during a no-report task involving perceptual suppression. Here, we report a separate LPFC population that exhibits task-phase related activity during the same task. The activity profile of these neurons could be captured as canonical response patterns (CRPs), with their peak amplitudes sequentially distributed across different task phases. Perceptually suppressed visual input had a negligible impact on sequential firing and functional connectivity structure. Importantly, task-phase related neurons were functionally segregated from the neuronal population, which encoded conscious perception. These results suggest that neurons exhibiting task-phase related activity operate in the LPFC concurrently with, but segregated from neurons representing conscious content during a no-report task involving perceptual suppression.

Vishal Kapoor et al. identify a population of cells in the lateral prefrontal cortex that exhibits task phase-related activity during a no-report task. This cell population is functionally segregated from the population encoding conscious perception, although the two operate in parallel.

Using High Frequency Transcranial Random Noise Stimulation to Modulate Face Memory Performance in Younger and Older Adults: Lessons Learnt From Mixed Findings

High-frequency transcranial random noise stimulation (tRNS) has been shown to improve a range of cognitive and perceptual abilities. Here we sought to examine the effects of a single session of tRNS targeted at the ventrolateral prefrontal cortices (VLPFC) on face memory in younger and older adults. To do so, we conducted three experiments. In Experiment 1, we found that younger adults receiving active tRNS outperformed those receiving sham stimulation (i.e., using a between-participant factor for stimulation condition; Experiment 1). This effect was not observed for object memory (car memory) in younger adults (Experiment 2), indicating that the effect is not a general memory effect. In Experiment 3, we sought to replicate the effects of Experiment 1 using a different design (within-participant factor of stimulation – active or sham tRNS to the same individual) and to extend the study by including older adult participants. In contrast to Experiment 1, we found that active tRNS relative to sham tRNS reduced face memory performance in both younger and older adults. We also found that the degree of decline in performance in the active tRNS relative to sham tRNS condition was predicted by baseline ability, with higher performing participants showing the largest decreases in performance. Overall, the results indicate that tRNS to the VLPFC modulates face memory, but that there may be performance and protocol specific moderators of this effect. We discuss these findings in the context of the broader literature showing the importance of individual variation in the outcome of non-invasive brain stimulation intervention approaches. We conclude that while tRNS may have potential as an intervention approach, generalizing from single experiment studies to wide application is risky and caution should be adopted in interpreting findings.

The utility and application of electrophysiological methods in the study of visual hallucinations

Visual hallucinations (VH) are a common symptom in multiple clinical and non-clinical populations. Although structural and functional neuroimaging has informed the understanding of VH, temporal resolution is limited. Electrophysiological techniques provide a complementary perspective on dynamic and temporal aspects of neural functioning, offering greater insight into the mechanisms underlying their formation. In this review we examine and critically evaluate the emerging evidence base utilising electrophysiological approaches in the study of VH. Overall, increased visual system excitability, dysfunctional visual processing and network connectivity, and cholinergic dysfunction have been consistently observed in VH-prone pathologies. However, a major limitation is in the lack of robust experimental studies and the reliance on single case reports. We conclude that electrophysiology provides tentative evidence for the contribution of bottom-up, top-down, and network dysfunction in the aetiology of VH, supporting several existing VH models. Furthermore, we discuss how electrophysiology has been directly utilised in specific clinical interventions for VH. Further exploration utilising electrophysiology in combination with, for example, neuroimaging will help better understand VH aetiology while aiding in the development of novel therapeutic interventions for this difficult to treat symptom.

Altered white matter connectivity associated with visual hallucinations following occipital stroke

INTRODUCTION

Visual hallucinations that arise following vision loss stem from aberrant functional activity in visual cortices and an imbalance of activity across associated cortical and subcortical networks subsequent to visual pathway damage. We sought to determine if structural changes in white matter connectivity play a role in cases of chronic visual hallucinations associated with visual cortical damage.

METHODS

We performed diffusion tensor imaging (DTI) and probabilistic fiber tractography to assess white matter connectivity in a patient suffering from continuous and disruptive phosphene (simple) visual hallucinations for more than 2 years following right occipital stroke. We compared these data to that of healthy age-matched controls.

RESULTS

Probabilistic tractography to reconstruct white matter tracts suggests regeneration of terminal fibers of the ipsilesional optic radiations in the patient. However, arrangement of the converse reconstruction of these tracts, which were seeded from the ipsilesional visual cortex to the intrahemispheric lateral geniculate body, remained disrupted. We further observed compromised structural characteristics, and changes in diffusion (measured using diffusion tensor indices) of white matter tracts in the patient connecting the visual cortex with frontal and temporal regions, and also in interhemispheric connectivity between visual cortices.

CONCLUSIONS

Cortical remapping and the disruption of communication between visual cortices and remote regions are consistent with our previous functional magnetic resonance imaging (fMRI) data showing imbalanced functional activity of the same regions in this patient (Rafique et al, 2016, Neurology, 87, 1493-1500). Long-term adaptive and disruptive changes in white matter connectivity may account for the rare nature of cases presenting with chronic and continuous visual hallucinations.

Influence of task instructions and stimuli on the neural network of face processing: An ALE meta-analysis

Many neuroimaging studies have investigated the neural correlates of face processing. However, the location of face-preferential regions differs considerably between studies, possibly due to the use of different stimuli or tasks. By using Activation likelihood estimation meta-analyses, we aimed to a) delineate regions consistently involved in face processing and b) to assess the influence of stimuli and task on convergence of activation patterns. In total, we included 77 neuroimaging experiments in healthy subjects comparing face processing to a control condition. Results revealed a core face-processing network encompassing bilateral fusiform gyrus (FFG), inferior occipital (IOG) gyrus, superior temporal sulcus/middle temporal gyrus (STS/MTG), amygdala, inferior frontal junction (IFJ) and gyrus (IFG), left anterior insula as well as pre-supplementary motor area (pre-SMA). Furthermore, separate meta-analyses showed, that while significant convergence across all task and stimuli conditions was found in bilateral amygdala, right IOG, right mid-FFG, and right IFG, convergence in IFJ, STS/MTG, right posterior FFG, left FFG and pre-SMA differed between conditions. Thus, our results point to an occipito-frontal-amygdalae system that is involved regardless of stimulus and attention, whereas the remaining regions of the face-processing network are influenced by the task-dependent focus on specific facial characteristics as well as the type of stimuli processed.

Mapping face categorization in the human ventral occipitotemporal cortex with direct neural intracranial recordings

The neural basis of face categorization has been widely investigated with functional magnetic resonance imaging (fMRI), identifying a set of face-selective local regions in the ventral occipitotemporal cortex (VOTC). However, indirect recording of neural activity with fMRI is associated with large fluctuations of signal across regions, often underestimating face-selective responses in the anterior VOTC. While direct recording of neural activity with subdural grids of electrodes (electrocorticography, ECoG) or depth electrodes (stereotactic electroencephalography, SEEG) offers a unique opportunity to fill this gap in knowledge, these studies rather reveal widely distributed face-selective responses. Moreover, intracranial recordings are complicated by interindividual variability in neuroanatomy, ambiguity in definition, and quantification of responses of interest, as well as limited access to sulci with ECoG. Here, we propose to combine SEEG in large samples of individuals with fast periodic visual stimulation to objectively define, quantify, and characterize face categorization across the whole VOTC. This approach reconciles the wide distribution of neural face categorization responses with their (right) hemispheric and regional specialization, and reveals several face-selective regions in anterior VOTC sulci. We outline the challenges of this research program to understand the neural basis of face categorization and high-level visual recognition in general.

Disentangling the Representation of Identity from Head View Along the Human Face Processing Pathway

Neural models of a distributed system for face perception implicate a network of regions in the ventral visual stream for recognition of identity. Here, we report a functional magnetic resonance imaging (fMRI) neural decoding study in humans that shows that this pathway culminates in the right inferior frontal cortex face area (rIFFA) with a representation of individual identities that has been disentangled from variable visual features in different images of the same person. At earlier stages in the pathway, processing begins in early visual cortex and the occipital face area with representations of head view that are invariant across identities, and proceeds to an intermediate level of representation in the fusiform face area in which identity is emerging but still entangled with head view. Three-dimensional, view-invariant representation of identities in the rIFFA may be the critical link to the extended system for face perception, affording activation of person knowledge and emotional responses to familiar faces.

Tuning face perception with electrical stimulation of the fusiform gyrus

The fusiform gyrus (FG) is an important node in the face processing network, but knowledge of its causal role in face perception is currently limited. Recent work demonstrated that high frequency stimulation applied to the FG distorts the perception of faces in human subjects (Parvizi et al. []: J Neurosci 32:14915-14920). However, the timing of this process in the FG relative to stimulus onset and the spatial extent of FG's role in face perception are unknown. Here, we investigate the causal role of the FG in face perception by applying precise, event-related electrical stimulation (ES) to higher order visual areas including the FG in six human subjects undergoing intracranial monitoring for epilepsy. We compared the effects of single brief (100 μs) electrical pulses to the FG and non-face-selective visual areas on the speed and accuracy of detecting distorted faces. Brief ES applied to face-selective sites did not affect accuracy but significantly increased the reaction time (RT) of detecting face distortions. Importantly, RT was altered only when ES was applied 100ms after visual onset and in face-selective but not place-selective sites. Furthermore, ES applied to face-selective areas decreased the amplitude of visual evoked potentials and high gamma power over this time window. Together, these results suggest that ES of face-selective regions within a critical time window induces a delay in face perception. These findings support a temporally and spatially specific causal role of face-selective areas and signify an important link between electrophysiology and behavior in face perception. Hum Brain Mapp 38:2830-2842, 2017. © 2017 Wiley Periodicals, Inc.

The effect of face patch microstimulation on perception of faces and objects

What is the range of stimuli encoded by face-selective regions of the brain? We asked how electrical microstimulation of face patches in macaque inferotemporal cortex affects perception of faces and objects. We found that microstimulation strongly distorted face percepts and that this effect depended on precise targeting to the center of face patches. While microstimulation had no effect on the percept of many non-face objects, it did affect the percept of some, including non-face objects whose shape is consistent with a face (for example, apples) as well as somewhat facelike abstract images (for example, cartoon houses). Microstimulation even perturbed the percept of certain objects that did not activate the stimulated face patch at all. Overall, these results indicate that representation of facial identity is localized to face patches, but activity in these patches can also affect perception of face-compatible non-face objects, including objects normally represented in other parts of inferotemporal cortex.

The Structural and Functional Organization of Cognition

This article proposes that what have been historically and contemporarily defined as different domains of human cognition are served by one of four functionally- and structurally-distinct areas of the prefrontal cortex (PFC). Their contributions to human intelligence are as follows: (a) BA9, enables our emotional intelligence, engaging the psychosocial domain; (b) BA47, enables our practical intelligence, engaging the material domain; (c) BA46 (or BA46-9/46), enables our abstract intelligence, engaging the hypothetical domain; and (d) BA10, enables our temporal intelligence, engaging in planning within any of the other three domains. Given their unique contribution to human cognition, it is proposed that these areas be called the, social (BA9), material (BA47), abstract (BA46-9/46) and temporal (BA10) mind. The evidence that BA47 participates strongly in verbal and gestural communication suggests that language evolved primarily as a consequence of the extreme selective pressure for practicality; an observation supported by the functional connectivity between BA47 and orbital areas that negatively reinforce lying. It is further proposed that the abstract mind (BA46-9/46) is the primary seat of metacognition charged with creating adaptive behavioral strategies by generating higher-order concepts (hypotheses) from lower-order concepts originating from the other three domains of cognition.

A Revised Neural Framework for Face Processing

Face perception relies on computations carried out in face-selective cortical areas. These areas have been intensively investigated for two decades, and this work has been guided by an influential neural model suggested by Haxby and colleagues in 2000. Here, we review new findings about face-selective areas that suggest the need for modifications and additions to the Haxby model. We suggest a revised framework based on (a) evidence for multiple routes from early visual areas into the face-processing system, (b) information about the temporal characteristics of these areas, (c) indications that the fusiform face area contributes to the perception of changeable aspects of faces, (d) the greatly elevated responses to dynamic compared with static faces in dorsal face-selective brain areas, and (e) the identification of three new anterior face-selective areas. Together, these findings lead us to suggest that face perception depends on two separate pathways: a ventral stream that represents form information and a dorsal stream driven by motion and form information.

Altered functional connectivity in lesional peduncular hallucinosis with REM sleep behavior disorder

Brainstem lesions causing peduncular hallucinosis (PH) produce vivid visual hallucinations occasionally accompanied by sleep disorders. Overlapping brainstem regions modulate visual pathways and REM sleep functions via gating of thalamocortical networks. A 66-year-old man with paroxysmal atrial fibrillation developed abrupt-onset complex visual hallucinations with preserved insight and violent dream enactment behavior. Brain MRI showed restricted diffusion in the left rostrodorsal pons suggestive of an acute ischemic stroke. REM sleep behavior disorder (RBD) was diagnosed on polysomnography. We investigated the integrity of ponto-geniculate-occipital circuits with seed-based resting-state functional connectivity MRI (rs-fcMRI) in this patient compared to 46 controls. Rs-fcMRI revealed significantly reduced functional connectivity between the lesion and lateral geniculate nuclei (LGN), and between LGN and visual association cortex compared to controls. Conversely, functional connectivity between brainstem and visual association cortex, and between visual association cortex and prefrontal cortex (PFC) was significantly increased in the patient. Focal damage to the rostrodorsal pons is sufficient to cause RBD and PH in humans, suggesting an overlapping mechanism in both syndromes. This lesion produced a pattern of altered functional connectivity consistent with disrupted visual cortex connectivity via de-afferentation of thalamocortical pathways.

Beyond the core face-processing network: Intracerebral stimulation of a face-selective area in the right anterior fusiform gyrus elicits transient prosopagnosia

According to neuropsychological evidence, a distributed network of regions of the ventral visual pathway - from the lateral occipital cortex to the temporal pole - supports face recognition. However, functional magnetic resonance imaging (fMRI) studies have generally confined ventral face-selective areas to the posterior section of the occipito-temporal cortex, i.e., the inferior occipital gyrus occipital face area (OFA) and the posterior and middle fusiform gyrus fusiform face area (FFA). There is recent evidence that intracranial electrical stimulation of these areas in the right hemisphere elicits face matching and recognition impairments (i.e., prosopagnosia) as well as perceptual face distortions. Here we report a case of transient inability to recognize faces following electrical stimulation of the right anterior fusiform gyrus, in a region located anteriorly to the FFA. There was no perceptual face distortion reported during stimulation. Although no fMRI face-selective responses were found in this region due to a severe signal drop-out as in previous studies, intracerebral face-selective event-related potentials and gamma range electrophysiological responses were found at the critical site of stimulation. These results point to a causal role in face recognition of the right anterior fusiform gyrus and more generally of face-selective areas located beyond the "core" face-processing network in the right ventral temporal cortex. It also illustrates the diagnostic value of intracerebral electrophysiological recordings and stimulation in understanding the neural basis of face recognition and visual recognition in general.

Intracerebral electrical stimulation of a face-selective area in the right inferior occipital cortex impairs individual face discrimination

During intracerebral stimulation of the right inferior occipital cortex, a patient with refractory epilepsy was transiently impaired at discriminating two simultaneously presented photographs of unfamiliar faces. The critical electrode contact was located in the most posterior face-selective brain area of the human brain (right "occipital face area", rOFA) as shown both by low- (ERP) and high-frequency (gamma) electrophysiological responses as well as a face localizer in fMRI. At this electrode contact, periodic visual presentation of 6 different faces by second evoked a larger electrophysiological periodic response at 6 Hz than when the same face identity was repeated at the same rate. This intracerebral EEG repetition suppression effect was markedly reduced when face stimuli were presented upside-down, a manipulation that impairs individual face discrimination. These findings provide original evidence for a causal relationship between the face-selective right inferior occipital cortex and individual face discrimination, independently of long-term memory representations. More generally, they support the functional value of electrophysiological repetition suppression effects, indicating that these effects can be used as an index of a necessary neural representation of the changing stimulus property.

Beyond the FFA: The role of the ventral anterior temporal lobes in face processing

Extensive research has supported the existence of a specialized face-processing network that is distinct from the visual processing areas used for general object recognition. The majority of this work has been aimed at characterizing the response properties of the fusiform face area (FFA) and the occipital face area (OFA), which together are thought to constitute the core network of brain areas responsible for facial identification. Although accruing evidence has shown that face-selective patches in the ventral anterior temporal lobes (vATLs) are interconnected with the FFA and OFA, and that they play a role in facial identification, the relative contribution of these brain areas to the core face-processing network has remained unarticulated. Here we review recent research critically implicating the vATLs in face perception and memory. We propose that current models of face processing should be revised such that the ventral anterior temporal lobes serve a centralized role in the visual face-processing network. We speculate that a hierarchically organized system of face processing areas extends bilaterally from the inferior occipital gyri to the vATLs, with facial representations becoming increasingly complex and abstracted from low-level perceptual features as they move forward along this network. The anterior temporal face areas may serve as the apex of this hierarchy, instantiating the final stages of face recognition. We further argue that the anterior temporal face areas are ideally suited to serve as an interface between face perception and face memory, linking perceptual representations of individual identity with person-specific semantic knowledge.

Intra- and interhemispheric connectivity between face-selective regions in the human brain

Neuroimaging studies have revealed a number of regions in the human brain that respond to faces. However, the way these regions interact is a matter of current debate. The aim of this study was to use functional MRI to define face-selective regions in the human brain and then determine how these regions interact in a large population of subjects (n = 72). We found consistent face selectivity in the core face regions of the occipital and temporal lobes: the fusiform face area (FFA), occipital face area (OFA), and superior temporal sulcus (STS). Face selectivity extended into the intraparietal sulcus (IPS), precuneus (PCu), superior colliculus (SC), amygdala (AMG), and inferior frontal gyrus (IFG). We found evidence for significant functional connectivity between the core face-selective regions, particularly between the OFA and FFA. However, we found that the covariation in activity between corresponding face regions in different hemispheres (e.g., right and left FFA) was higher than between different face regions in the same hemisphere (e.g., right OFA and right FFA). Although functional connectivity was evident between regions in the core and extended network, there were significant differences in the magnitude of the connectivity between regions. Activity in the OFA and FFA were most correlated with the IPS, PCu, and SC. In contrast, activity in the STS was most correlated with the AMG and IFG. Correlations between the extended regions suggest strong functional connectivity between the IPS, PCu, and SC. In contrast, the IFG was only correlated with the AMG. This study reveals that interhemispheric as well as intrahemispheric connections play an important role in face perception.

Empirical support for higher-order theories of conscious awareness

Higher-order theories of consciousness argue that conscious awareness crucially depends on higher-order mental representations that represent oneself as being in particular mental states. These theories have featured prominently in recent debates on conscious awareness. We provide new leverage on these debates by reviewing the empirical evidence in support of the higher-order view. We focus on evidence that distinguishes the higher-order view from its alternatives, such as the first-order, global workspace and recurrent visual processing theories. We defend the higher-order view against several major criticisms, such as prefrontal activity reflects attention but not awareness, and prefrontal lesion does not abolish awareness. Although the higher-order approach originated in philosophical discussions, we show that it is testable and has received substantial empirical support.

Spatio temporal dynamics of face recognition

To better understand face recognition, it is necessary to identify not only which brain structures are implicated but also the dynamics of the neuronal activity in these structures. Latencies can then be compared to unravel the temporal dynamics of information processing at the distributed network level. To achieve high spatial and temporal resolution, we used intracerebral recordings in epileptic subjects while they performed a famous/unfamiliar face recognition task. The first components peaked at 110 ms in the fusiform gyrus (FG) and simultaneously in the inferior frontal gyrus, suggesting the early establishment of a large-scale network. This was followed by components peaking at 160 ms in 2 areas along the FG. Important stages of distributed parallel processes ensued at 240 and 360 ms involving up to 6 regions along the ventral visual pathway. The final components peaked at 480 ms in the hippocampus. These stages largely overlapped. Importantly, event-related potentials to famous faces differed from unfamiliar faces and control stimuli in all medial temporal lobe structures. The network was bilateral but more right sided. Thus, recognition of famous faces takes place through the establishment of a complex set of local and distributed processes that interact dynamically and may be an emergent property of these interactions.

Processing emotional expression and facial identity in schizophrenia

Previous studies showed that schizophrenic patients have a deficit in facial information processing. The purpose of the present study was to test the abilities of patients with schizophrenia and normal controls in emotion and identity matching when these two dimensions were varied orthogonally. Subjects (20 schizophrenic patients and 20 controls) had to report if two faces had the same emotion or belonged to the same person. When the task concerned one type of information (i.e. emotion or identity), the other one was either constant (same person or same emotion) or changed (different person or different emotion). Schizophrenic patients performed worse than controls for both kinds of facial information. Their deficit was more important when the secondary factor was changed. In particular, they performed at chance level when they had to match one emotion expressed by two distinct persons. Finally, correlation analysis indicated that performance/deficit in identity and emotion matching co-varied and that in such tasks performance is negatively correlated with the severity of negative symptoms in patients. Schizophrenic patients present a generalised deficit for accessing facial information. A facial emotion and an identity-processing deficit are related to negative symptoms. Implications for face-recognition models are discussed.

Effects of emotion and identity on facial affect processing in schizophrenia

We used facial affect labeling and matching tasks to study effects of (1) emotion and (2) identity on facial affect processing in patients with remitted schizophrenia (n=30) compared with healthy controls (n=30). The patients (1) had a specific deficit for labeling facial affects of sadness and anger but not happiness, disgust and fear; they (2) performed as well as controls in matching facial affects in one face but were impaired in matching facial affects in two different faces. The patients' impairment in facial affect processing may be emotion-specific. The effects of identity on facial affect processing are discussed in the light of several hypotheses (a deficit of context processing, a global-local processing impairment or a selective attention deficit), and may be related to frontal, prefrontal or amygdala dysfunctions.

The Influence of Repetition and Famousness on the Intracranially Recorded Temporobasal N200

It is still a matter of debate at which time point faces are recognized as familiar, with some studies claiming a relatively early face recognition and others later effects of familiarity. The authors report on effects of famousness of depicted persons and stimulus repetition on intracranially recorded event-related potentials. Famousness resulted in an increased latency of the N200 component, as well as in an increased amplitude of a later long-lasting potential (N700). In contrast, repetition led to an increased amplitude of the N200 but no increase of its latency. They suppose that the recognition of faces becomes observable within the N200 latency range and that the increased N200 latency reflects a feature processing additional to the holistic face processing.

Semiologic Value of Ictal Autoscopy

PURPOSE

Autoscopy is a pathologic perception of one's body or one's face image within space, either from an internal ("as in a mirror") or from an external ("out-of-body experience") point of view. Among various psychiatric and neurologic disorders, partial epilepsy is the main etiology. However, the significance of this rare ictal symptom remains controversial. We report this phenomenon in three epilepsy patients and discuss its semiologic value and neuropsychological significance.

METHODS

Interictal EEG and/or video-EEG monitoring was performed, as well as neuropsychological examination and cerebral magnetic resonance imaging (MRI).

RESULTS

The three patients had a lesion involving, or limited to, the right parietal region on cerebral MRI. All three patients experienced autoscopy associated with other ictal signs supporting a right parietal lobe origin of seizures. In one patient, seizure origin was documented with video and surface EEG ictal recordings.

CONCLUSIONS

Autoscopy was shown to have an ictal mechanism and was associated with seizures arising from the nondominant parietal region. We hypothesize that ictal autoscopy may result from disruption of the normal integration of body representation.

Long-latency ERPs and recognition of facial identity

N400 brain event-related potential (ERP) is a mismatch negativity originally found in response to semantic incongruences of a linguistic nature and is used paradigmatically to investigate memory organization in various domains of information, including that of faces. In the present study, we analyzed different mismatch negativities evoked in N400-like paradigms related to recognition of newly learned faces with or without associated verbal information. ERPs were compared in the following conditions: (1) mismatching features (eyes-eyebrows) using a facial context corresponding to the faces learned without associated verbal information ("pure" intradomain facial processing); (2) mismatching features using a facial context corresponding to the faces learned with associated occupations and proper names ("nonpure" intradomain facial processing); (3) mismatching occupations using a facial context (cross-domain processing); and (4) mismatching names using an occupation context (intradomain verbal processing). Results revealed that mismatching stimuli in the four conditions elicited a mismatch negativity analogous to N400 but with different timing and topographical patterns. The onset of the mismatch negativity occurred earliest in Conditions 1 and 2, followed by Condition 4, and latest in Condition 3. The negativity had the shortest duration in Task 1 and the longest duration in Task 3. Bilateral parietal activity was confirmed in all conditions, in addition to a predominant right posterior temporal localization in Condition 1, a predominant right frontal localization in Condition 2, an occipital localization in Condition 3, and a more widely distributed (although with posterior predominance) localization in Condition 4. These results support the existence of multiple N400, and particularly of a nonlinguistic N400 related to purely visual information, which can be evoked by facial structure processing in the absence of verbal-semantic information.

History and future directions of human brain mapping and functional neuroimaging

It has long been known that there is some degree of localisation of function in the human brain, as indicated by the effects of traumatic head injury. Work in the middle of the 20th century, notably the direct cortical stimulation of patients during neurosurgery, suggested that the degree and specificity of such localisation of function were far greater than had earlier been imagined. One problem with the data based on lesions and direct stimulation was that the work depended on the study of what were, by definition, damaged brains. During the second half of the 20th century, a collection of relatively non-invasive tools for assessing and localising human brain function in healthy volunteers has led to an explosion of research in what is often termed "Brain Mapping". The present article reviews some of the history associated with these tools, but emphasises the current state of development with speculation about the future.